The present invention relates to an actuation system for a transmission synchronizer, and more particularly relates to an actuation system for such a transmission synchronizer which can operate automatically and which yet can provide smooth and accurate engagement of speed stages of the transmission.
In a transmission which includes one or more synchronizers, such a synchronizer (which may be for example of a so called Borg Warner type) typically includes a first member which is pushed against a second member in order to synchronize the relative rotational speeds of two mutually rotating elements of the transmission, usually as a preliminary to securely engaging these elements rotationally together. For example, in a particular example of construction, in the case that it is desired to rotationally engage a gear wheel to a shaft on which it is rotatably mounted, said gear wheel and said shaft being currently in the state of being rotated at different rotational speeds but the rotational speed of at least one of them being able to be progressively altered by a certain moderate applied torque, then a synchronizer sleeve rotationally coupled to the shaft but axially free to slide thereon is pushed against a ring member which is pushed against a cone member which is rotationally coupled to the gear wheel which is axially fixed in position, and by the compressed sandwiching of these members between the synchronizer sleeve which is being axially pushed and the gear wheel rotating with respect thereto a mutual torque or couple is generated between the shaft and the gear wheel in the relative rotational direction to bring their absolute rotational speeds to be the same, in other words in the relative rotational direction to bring their relative rotational speed to zero. When this has happened, in other words when the synchronizer action has brought the gear wheel and the shaft to rotate at the same rotational speed, then a different mechanism incorporating for example a key mechanism securely and positively rotationally connects the gear wheel to the shaft, without relying on the frictional effect of the above described synchronizer parts; but this is not directly relevant to the actual synchronizing action of the synchronizer. The synchronizer sleeve is typically driven in the axial direction by a fork engaged thereto which is slidably mounted on a fork shaft or the like. Such a fork may be manually driven by the hand of a vehicle operator pushing a gear lever, or may be power driven by an actuator, in the case of the transmission being an automatic transmission, for example.
Now, the load, frictional force, heat, and stress generated in the various members of the synchronizer, i.e. in the above example in the synchronizer sleeve, the ring member, and the cone member, are generally the greater the greater is the relative rotational speed of the members whose rotation is to be synchronized, i.e. in the above example the relative rotational speed of the shaft and the gear wheel, and are also generally the greater the greater is the pressure with which the synchronizer sleeve is pushed, i.e. in the above example the greater is the compression force squeezing the parts together. In order to preserve the service life of the synchronizer mechanism as a whole the load, frictional force, heat, and strain generated in the members of the synchronizer must be kept within acceptable limits, since otherwise the mechanism will quickly be deteriorated and will suffer an unacceptable loss of synchronization function. Now, in the case that the synchronizer sleeve is axially manually driven by the hand of a vehicle operator pushing a gear lever, then an almost unconscious feedback relating to the back pressure from the interaction of the synchronizer sleeve and the ring member and the cone member, etc., operates to help to ensure that not too rough an action is exerted, in other words that a slick and smooth synchronizing action is available, at least in the case of a skilled vehicle operator who is in mental tune with the operation of the machinery; but, in the case that the axial movement of the synchronizer sleeve is performed mechanically by the action of an actuator, then the unconscious yet subtle regulatory action of human operation and touch is not available, and in the prior art it has been a real problem to secure smooth and slick synchronizer action for engaging speed stages of the transmission, without running the risk that the synchronizer sleeve should be abruptly and over violently jammed in the direction of the gear wheel, thus "crunching the gears" and damaging the various parts of the synchronizer by generating too much heat and frictional stress therein, nor running the counterpart risk that by pushing the synchronizer sleeve too weakly towards the gear wheel the synchronization action should be performed so slowly that steady buildup of frictional heat in the synchronizer parts should similarly damage the synchronizer.
The difficulty of regulating this synchronizer action is made the greater, because the synchronizer is operated in a wide range of operational conditions, with regard to rotational speeds of the two members thereof, load being transmitted thereby, and the like.